Many of the medical and scientific terms used in this summary are found in the NCI Dictionary of Genetics Terms. When a linked term is clicked, the definition will appear in a separate window.

Many of the genes and conditions described in this summary are found in the Online Mendelian Inheritance in Man (OMIM) database. When OMIM appears after a gene name or the name of a condition, click on OMIM for a link to more information.

Among women, breast cancer is the most commonly diagnosed cancer after nonmelanoma skin cancer, and it is the second leading cause of cancer deaths after lung cancer. In 2013, an estimated 234,580 new cases will be diagnosed, and 40,030 deaths from breast cancer will occur.[1] The incidence of breast cancer, particularly for estrogen receptor–positive cancers occurring after age 50 years, is declining and has declined at a faster rate since 2003; this may be temporally related to a decrease in hormone replacement therapy (HRT) following early reports from the Women's Health Initiative.[2] Ovarian cancer is the ninth most common cancer, with an estimated 22,240 new cases in 2013, but is the fifth most deadly, with an estimated 14,030 deaths in 2013.[1] (Refer to the PDQ summaries on Breast Cancer Treatment and Ovarian Epithelial Cancer Treatment for more information on breast cancer and ovarian cancer rates, diagnosis, and management.)

A possible genetic contribution to both breast and ovarian cancer risk is indicated by the increased incidence of these cancers among women with a family history (see the Family History as a Risk Factor for Breast Cancer and the Family History as a Risk Factor for Ovarian Cancer sections below), and by the observation of some families in which multiple family members are affected with breast and/or ovarian cancer, in a pattern compatible with an inheritance of autosomal dominant cancer susceptibility. Formal studies of families (linkage analysis) have subsequently proven the existence of autosomal dominant predispositions to breast and ovarian cancer and have led to the identification of several highly penetrant genes as the cause of inherited cancer risk in many families. (Refer to the PDQ summary Cancer Genetics Overview for more information on linkage analysis.) Mutations in these genes are rare in the general population and are estimated to account for no more than 5% to 10% of breast and ovarian cancer cases overall. It is likely that other genetic factors contribute to the etiology of some of these cancers.